通过Windows DShow获取设备名、支持的编解码及视频size列表实现

之前在https://blog.csdn.net/fengbingchun/article/details/102641967中介绍过通过DShow获取Camera视频的实现，即调用VideoCapture类。在OpenCV的VideoCapture类中并没有提供获取Camera设备列表、支持的编解码类型列表及支持的video size列表接口，这里基于已有的VideoCapture类增加对这些的实现。

获取Camera设备名：在videoInput类中有两个函数，一个是getDeviceCount用于获取设备数，一个是getDeviceName用于根据索引获取设备名。在CvCaputreCAM_DShow类中增加函数getDevicesList，实现如下，在此函数中调用videoInput中的getDeviceCount和getDeviceName。

bool CvCaptureCAM_DShow::getDevicesList(std::map<int, std::string>& devicelist) const
{devicelist.clear();for (int i = 0; i < VI.getDeviceCount(); ++i) {devicelist[i] = VI.getDeviceName(i);}return true;
}

增加一个对外调用的接口get_camera_names，实现如下：

bool FBC_EXPORTS get_camera_names(std::map<int, std::string>& names)
{VideoCapture capture(0);if (!capture.isOpened()) {fprintf(stderr, "fail to open capture\n");return false;}return capture.getDevicesList(names);
}

获取Camera支持的编解码类型和video size：这部分的实现参考了FFmpeg中的源码libavdevice/dshow.c，并把其中的一些code移了过来。首先在videoInput类中增加一个变量infolist，用于存放设备索引名、编解码类型、视频size信息；增加一个函数getCodecAndVideoSize，用于实现获取编解码和video size；增加一个getCodecList用于供CvCaptureCAM_DShow调用获取编解码列表；增加一个getVideoSizeList用于供CvCaptureCAM_DShow调用获取video size列表。CvCaptureCAM_DShow中也有对应的这两个函数，用于供VideoCapture调用。它们的实现如下：执行完VD->streamConf->GetStreamCaps后，结构体scc中的MinOutputSize和MaxOutputSize成员变量值即是video size。通过计算结构体pmtConfig中的BITMAPINFOHEADER即可获取codec type。

void videoInput::getCodecAndVideoSize(videoDevice *VD)
{infolist[VD->myID].clear();int iCount = 0;int iSize = 0;HRESULT hr = VD->streamConf->GetNumberOfCapabilities(&iCount, &iSize);if (hr != S_OK) {fprintf(stderr, "fail to get number of capabilities\n");return;}if (iSize == sizeof(VIDEO_STREAM_CONFIG_CAPS)) {std::map<int, std::map<int, std::set<std::vector<int>>>> info;//For each format type RGB24 YUV2 etcfor (int iFormat = 0; iFormat < iCount; iFormat++) {VIDEO_STREAM_CONFIG_CAPS scc;AM_MEDIA_TYPE *pmtConfig;hr = VD->streamConf->GetStreamCaps(iFormat, &pmtConfig, (BYTE*)&scc);if (SUCCEEDED(hr)){//his is how many diff sizes are available for the formatint stepX = scc.OutputGranularityX;int stepY = scc.OutputGranularityY;//Don't want to get stuck in a loopif (stepX < 1 || stepY < 1) continue;std::vector<int> size_min{ scc.MinOutputSize.cx, scc.MinOutputSize.cy }, size_max{ scc.MaxOutputSize.cx, scc.MaxOutputSize.cy };VIDEOINFOHEADER* pVih = reinterpret_cast<VIDEOINFOHEADER*>(pmtConfig->pbFormat);BITMAPINFOHEADER* bih = &pVih->bmiHeader;const AVCodecTag *const tags[] = { avformat_get_riff_video_tags(), NULL };enum AVPixelFormat pix_fmt = dshow_pixfmt(bih->biCompression, bih->biBitCount);if (pix_fmt == AV_PIX_FMT_NONE) {enum AVCodecID codec_id = av_codec_get_id(tags, bih->biCompression);if (codec_id != AV_CODEC_ID_NONE) {if (codec_id == AV_CODEC_ID_MJPEG) {info[VD->myID][VIDEO_CODEC_TYPE_MJPEG].insert(size_min);info[VD->myID][VIDEO_CODEC_TYPE_MJPEG].insert(size_max);}else if (codec_id == AV_CODEC_ID_H264) {info[VD->myID][VIDEO_CODEC_TYPE_H264].insert(size_min);info[VD->myID][VIDEO_CODEC_TYPE_H264].insert(size_max);}else if (codec_id == AV_CODEC_ID_H265) {info[VD->myID][VIDEO_CODEC_TYPE_H265].insert(size_min);info[VD->myID][VIDEO_CODEC_TYPE_H265].insert(size_max);}}}else {info[VD->myID][VIDEO_CODEC_TYPE_RAWVIDEO].insert(size_min);info[VD->myID][VIDEO_CODEC_TYPE_RAWVIDEO].insert(size_max);}MyDeleteMediaType(pmtConfig);}}for (auto codec_id = 0; codec_id < info[VD->myID].size(); ++codec_id) {for (auto it = info[VD->myID][codec_id].cbegin(); it != info[VD->myID][codec_id].cend(); ++it) {std::string size = std::to_string((*it)[0]);size += "x";size += std::to_string((*it)[1]);infolist[VD->myID][codec_id].push_back(size);}}}else {fprintf(stderr, "fail to get codec and video size\n");return;}
}bool videoInput::getCodecList(int device_id, std::vector<int>& codecids)
{codecids.clear();if (infolist[device_id].size() == 0) return false;for (auto it = infolist[device_id].cbegin(); it != infolist[device_id].cend(); ++it) {codecids.push_back(it->first);}return true;
}bool videoInput::getVideoSizeList(int device_id, int codec_id, std::vector<std::string>& sizelist)
{if (device_id >= getDeviceCount()) return false;sizelist = this->infolist[device_id][codec_id];return true;
}

OpenCV中的VideoCapture类中虽然有接收设备名的接口，但是好像并不能运行，只能通过设备索引来获取视频。在一台PC机上插入多个USB摄像头时并不清楚哪个索引对应哪个设备名，这里对VideoCapture(const std::string& filename)的实现进行了修改，使其可以通过输入设备名获取视频，实现如下：首先通过索引0获取到设备列表，然后根据输入的设备名在设备列表中是否可以映射到对应的索引值，如果有匹配的，则再通过对应的索引值打开设备。

bool VideoCapture::open(const std::string& filename)
{if (isOpened()) release();open(0);if (!cap) return false;std::map<int, std::string> devices_name;cap->getDevicesList(devices_name);if (devices_name.size() == 0) return false;if (isOpened()) release();int device = -1;for (auto it = devices_name.cbegin(); it != devices_name.cend(); ++it) {if (filename.compare((*it).second) == 0)device = (*it).first;}if (device == -1) return false;return open(device);
}

测试代码如下：

#include "fbc_cv_funset.hpp"
#include <videocapture.hpp>
#include <opencv2/opencv.hpp>int test_get_camera_info()
{
#ifdef _MSC_VERstd::map<int, std::string> camera_names;fbc::get_camera_names(camera_names);fprintf(stdout, "camera count: %d\n", camera_names.size());for (auto it = camera_names.cbegin(); it != camera_names.cend(); ++it) {fprintf(stdout, "camera index: %d, name: %s\n", (*it).first, (*it).second.c_str());}fbc::VideoCapture capture(0);if (!capture.isOpened()) {fprintf(stderr, "fail to open capture\n");return -1;}std::vector<int> codecids;capture.getCodecList(codecids);fprintf(stdout, "support codec type(video_codec_type_t: 0: h264; 1: h265; 2: mjpeg; 3: rawvideo): ");for (auto i = 0; i < codecids.size(); ++i) {fprintf(stdout, "%d  ", codecids[i]);}fprintf(stdout, "\n");std::vector<std::string> sizelist;int codec_type = fbc::VIDEO_CODEC_TYPE_MJPEG;capture.getVideoSizeList(codec_type, sizelist);fprintf(stdout, "codec type: %d, support video size list:(width*height)\n", codec_type);for (auto it = sizelist.cbegin(); it != sizelist.cend(); ++it) {fprintf(stdout, "\t%s\n", (*it).c_str());}return 0;
#elsefprintf(stderr, "Error: only support windows platform\n");return -1;
#endif
}

执行结果如下：

GitHub：https://github.com//fengbingchun/OpenCV_Test